1. Technical Field
The present invention relates to ball screws, and more particularly to an internal-circulation-type ball screw that provides good durability and cyclical stability.
2. Description of Related Art
In the art of ball screws, there are many approaches to internal circulation of balls. For example, Japan Patent No. 2010-090953 involves forming a circulation groove at the surface of the screw along which balls can circulate. However, since the circulation groove only strides across a single pitch, when the lead is low and close to the ball's diameter, it tends to impact the balls and get damaged because the thread's crest is thin. On the other hand, Taiwan Patent No. M472136 also uses a circulation groove that strides across a single pitch. In addition to the same problem as mentioned previously, an interrupted-thread designed when used can adds challenges to special configuration. Japan Patent No. 2005-201347 differently uses a segment difference generated at the surface of the screw to guide the balls. Nevertheless, the technology generally suffers from difficult processing and poor cyclical stability.